The present invention relates to an optical illumination device for an electrophotographic copying apparatus and more specifically relates to an optical illumination device having an exposure regulating means.
Automatic illumination devices for electrophotographic copying machines wherein light is projected from a lamp onto an original document, the amount of light reflected from said document is detected, and the amount of light exposure to the photosensitive member is automatically controlled in correspondence with the detection signal volume are well known.
Japanese laid-open utility mode Patents Sho 60-76254 and Sho 61-6837, for example, disclose illumination devices which expose the photosensitive member to the light emitting from an illumination source which is reflected from an original document via a condensing/light-transmitting array, and wherein the reflected light from the original document disposed immediately above said array is condensed by lenses so as to provide incident rays to the photoreceptor disposed outside the optical path toward the photosensitive member.
However, these illumination devices have a disadvantage in that the response of the illumination controls is poor because a portion of the light reflected to the photosensitive member is also provided to the photoreceptor.
Japanese laid-open Patent Sho 56-110961 attempts to resolve this disadvantage. The illumination device disclosed in this has an elliptical reflecting mirror which directs the light from the light source to the original document, said reflecting mirror also being provided with an aperture in one portion. The reflecting mirror condenses the light projected to the document to be scanned, and the aperture of said reflecting mirror projects light to the document portion directly preceding the scan. This illumination device transmits reflected light from the document portion immediately preceding the scan via an optical fiber, detects the amount of reflected light by light receiving elements, and adjusts the exposure by comparing the detection signal volume with a predetermined reference value.
Thus, the illumination control response delay can be prevented because this illumination device adjusts the light source by detecting light reflected from one portion of the original document immediately prior to the scan and then adjusts the light source accordingly. However, illumination is unwarrantedly more than required because of the aperture formed on a portion of the elliptical reflecting mirror, and the device itself is made more costly still by the use of optical fiber as the light transmission means. A further disadvantage lies in the complexity of the structure from the light source to the photoreceptor.